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Reduction of unusual iron-sulfur clusters in the H-2-sensing regulatory Ni-Fe hydrogenase from Ralstonia eutropha H16
Citation key Buhrke2005
Author Buhrke, T. and Loscher, S. and Lenz, O. and Schlodder, E. and Zebger, I. and Andersen, L. K. and Hildebrandt, P. and Meyer-Klaucke, W. and Dau, H. and Friedrich, B. and Haumann, M.
Pages 19488–19495
Year 2005
Journal Journal Of Biological Chemistry
Volume 280
Number 20
Abstract The regulatory Ni-Fe hydrogenase (RH) from Ralstonia eutropha functions as a hydrogen sensor. The RH consists of the large subunit HoxC housing the Ni-Fe active site and the small subunit HoxB containing Fe-S clusters. The heterolytic cleavage of H-2 at the Ni-Fe active site leads to the EPR-detectable Ni-C state of the protein. For the first time, the simultaneous but EPR-invisible reduction of Fe-S clusters during Ni-C state formation was demonstrated by changes in the UV-visible absorption spectrum as well as by shifts of the iron K-edge from x-ray absorption spectroscopy in the wildtype double dimeric RHWT [HoxBC](2) and in a monodimeric derivative designated RHstop lacking the C-terminal 55 amino acids of HoxB. According to the analysis of iron EXAFS spectra, the Fe-S clusters of HoxB pronouncedly differ from the three Fe-S clusters in the small subunits of crystallized standard Ni-Fe hydrogenases. Each HoxBC unit of RHWT seems to harbor two [2Fe-2S] clusters in addition to a 4Fe species, which may be a [4Fe-3S-3O] cluster. The additional 4Fe-cluster was absent in RHstop. Reduction of Fe-S clusters in the hydrogen sensor RH may be a first step in the signal transduction chain, which involves complex formation between [HoxBC](2) and tetrameric HoxJ protein, leading to the expression of the energy converting Ni-Fe hydrogenases in R. eutropha.
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